I’m at 95.2% and I agree with Antheus.
Just to add to what Antheus said though, it’s the fog of war on the map for all explorable areas.
Meaning areas where there are no zones, which is a lot of Tyria, doesn’t count towards the 100%.
And although it is possible that I did explore all of pre-searing with my main mapping character (it’s been so long I don’t remember), I don’t think it affects the 100%.
Hopefully this advice helps for those trying to increase their exploration percent, but most people tend to miss the areas around the bonuses for missions. Even some of the maps by MOOMANiBE have patches that haven’t been uncovered. Some of these cases happen because once a person gets the bonus, they feel they’ve finished.
Dunes of Despair is a good example of this. There is a big patch missing in MOOMANiBE’s map around the bonus area.
Luckily for me I know what patches I need to uncover to get the last 4.8% since I have them uncovered on another character, and yah, two patches are in a couple mission bonus areas. I just need some free time to play
Although it might be a bit tedious, the best way I know of to see what you’re missing is by comparing your map with online maps.